What is file extension?

Some file systems place name extensions as a feature of that system. The name of a system may be restricted to the length and format of the extension. In other cases, file name extensions or file extensions are considered part of the file name without too much distinction.

What is file extension?

File extensions or file name extensions are letters displayed immediately after the last paragraph in the file name. For example, the file extension.txt has an extension of .txt. This extension lets the operating system know what kind of file it is and what program will run when you open this file.

The rule on how to format an extension is to start with a dot and have at least one character. For most cases, the file extension consists of three characters, usually letters or numbers. Some examples of file extensions include .txt, .mp3, .jpg and .gz, which will in turn represent text files, mp3 files, jpeg image files and compressed files with a gzip program. As you can see, the actual extension provides basic information about file types.

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When trying to determine the extension of a file, it is important to remember that the extension is simply the last paragraph in a file name and includes characters. If there are no sections in a file name, it does not have an extension. To make it easier to understand what file extensions are, please see the examples in the table below:

File name Extensions Note report_card.txt .txt The extension is the character after the dot Terminal.app .app The extension is the character after the dot Postcard.pdf.exe .exe This file name is a little bit complicated more confused than usual, there are up to 2 paragraphs after the dot. But remember the principle: Extensions are just the last paragraph (including dots and characters).

As mentioned, an operating system knows which program to use to view, print or edit a specific file by looking at its extension. It can do this because each operating system in the configuration has a default mapping between a file extension and a specific program. Using this information, when a user clicks on a file, reads the file extension and then launches the mapped application. Normally, if the extension is not known to the operating system or no application mapping exists, it will prompt the user to specify the program to open the file.

By default, Windows and Mac OS do not display file extensions. To view the file extensions, you first need to enable them or you can also change the program that the operating system uses to open a specific extension.

How to change the program associated with the file extension

As mentioned, the file extension is mapped to a specific program so that when you try to open the file, the operating system will know which application will launch. You may want to change the default link sometimes, using another program to automatically open the file. For example, when you open an image file on Windows, it will default to the built-in Windows Photo Viewer. In the future if you find a new program and want to use it to open image files, you can change the links for image files to open them with the new program.

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How malware uses extensions to trick users into opening files containing viruses

A common trick that malware will use to trick you into running an infected program is to send an email attachment with the file name containing two dots in it. For example sales_report.xls.exe. As you can see the file has an .exe extension, which means it is an executable file. But you should not run this program.

What happens if the .exe extension is removed from the file name and becomes sales_reports.xls? It's a name that looks harmless, and if you get this file from a friend, you'll think it's safe and double-click it. When you double-click it, the file will be executed later and infect the virus to your computer.

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Malware creators know that this method can fool many people because by default, Windows does not show users file extensions. Therefore, if you have not enabled the file extension, the window will only show you everything before the last paragraph in the file name and you may think it is the full name. So, this is a common tactic for malware spreaders or spammers because they know that Microsoft will remove the last part and make the file seem safe.

Therefore, it is important to always display file extensions in Windows so that you are not fooled by this tip.

Below is a list of common file extensions that you can find on your computer or over the Internet.

Audio file extension

Extensions

Describe

.aif Audio Interchange File is the most commonly used audio file format on Apple Macintosh computer systems. .m3u M3U files are used to store multimedia playlists. .mp3 MP3 File is the most common file format used to store digital audio, used on computers and digital media devices. .ra Audio file created by RealAudio. .wav WAV or Waveform Audio File Format is an audio file format used to store audio on a PC. .wma Windows Media Audio or WMA is an audio file format developed by Microsoft.

Video file extension

Extensions Description .avi Audio Video Interleave or AVI is a video and audio file created by Microsoft. .flv Flash .mov video file Apple QuickTime movie. .mp4 .mpg video file MPEG .wmv video file Windows Media Video or WMV is a video file created by Microsoft.

Image file extension

Extensions Description .bmp Bitmap or BMP is an image file used to store digital bitmap images. These files are usually found in Windows. .cur CUR file format is used to store pointers that are not animated in Windows. .ico ICO file format is used to store computer icons in Microsoft Windows. .gif Graphics Interchange Format or GIF is an image file format created by Compuserve. This is a popular format on computers and the Internet. .jpg JPEG image file is a popular file found on computers and the Internet. .jpeg Another extension corresponding to a JPEG image file. . Portable Network Graphic or PNG file is an image file created to replace the GIF file. This is a popular format on computers and the Internet. .psd Photoshop Document or PSD is the file used to store images created by Adobe Photoshop. .raw The raw image format is often used by digital cameras to store images in the currently unprocessed format. .tif Tagged Image File Format or TIF is a picture that is often used by artists and photographers.

Workplace application extensions and text files

Extension Description .csv Comma Separated Value or CSV is a text file containing commas separated by commas. .doc Word Document or DOC is the extension that Word will save its document. .docx Starting Word 2007, the .docx file format becomes the standard file that Microsoft Word will save. .log The text file usually contains a text log of the application or computer process performed or transmitted. .pdf Portable Document Format or PDF is a file format created by Adobe Systems. This file format is used to create documents that contain a specific fixed layout regardless of whether the operating system or application is open. .pps Microsoft PowerPoint presentation file. .ppt PowerPoint Document or PPT is an extension that PowerPoint will save the document. .pptx Starting with PowerPoint 2007, the .pptx file format becomes the standard file that Microsoft PowerPoint will save the file. .rtf Rich Text Format or RTF created by Microsoft allows formatting text, such as bold or underlined, in text documents. .txt A text file is a file that contains text data without any format. .wpd Standard file format for storing WordPerfect documents. .wps A Microsoft Works document. .xlr Microsoft Works spreadsheet file. .xls Excel Document or XLS is the standard file format that Microsoft Excel will save the file, but has been changed to .xlsx starting in Excel 2007. .xlsx Starting in Excel 2007, the .docx file format becomes a standard file. but Microsoft Excel will save the file.

Zip file extension or archive utility

Extension Description .7z The original archive format was created by 7-Zip archive. .bz2 File compressed with bzip2. This file format is commonly used on Linux and Unix systems. The .cab Cabinet or CAB is a compressed archive format used by Microsoft. .deb Debian Software Package or DEB is a file used to install applications in Debian. .gz File is gzip compressed. This file format is commonly used on Linux and Unix systems. .pkg Package or PKG is a file used to install applications in Apple OS. .rar Roshal Archive or RAR is a storage format used by WinRar. .rpm RPM Package Manager or RPM is a file used to install applications in the Linux operating system. .sit Stuffit or SIT is a zip file developed by Stuffit. .sitx Stuffit X-compressed or SITX is a compressed file from Stuffit. .tar An archive file created by the Tar utility. This type of file format is often found on Linux and Unix operating systems. .tar.gz This is a tar file compressed with the Gzip utility. .zip ZIP file is a compressed archive file. This is the most popular compression format on computers and on the Internet. Windows and Macintosh have integrated support for Zip files. .Z A file has been compressed with the compress command of Linux or Unix.

Web and Internet extensions

Extensions Description .css Cascading Style Sheets or CSS is a cascading style file, describing how HTML is displayed in an HTML file. .htm Hypertext Markup Language or HTML is a file containing HTML markup language, used to display formatted content on web pages. .html Similar to .htm .js Javascript or JS is a file that contains scripts that will be executed by your web browser. .part When you download a file, the downloaded information is stored in a file part until the file is downloaded. Once completed, the file will be renamed to a real name.

Image extension on the drive

Extensions Description Apple Disk Image .dmg or DMG is a file that contains the archive of a hard disk or CD / DVD. .iso ISO image file is an archive of an optical drive, such as a CD or DVD drive.

E-mail extension

Extensions Description .eml Some applications such as Microsoft Outlook Express, Windows Mail and Mozilla Thunderbird save your e-mail as individual eml files on your hard drive. If you double-click them, your mail application will open each email it represents. .emlx Similar to the .eml file, but for Apple Mail messages. .mbx File MBX represents a specific directory in the mail application. The name of the file will usually be named after the actual directory it represents. .pst Microsoft Outlook data file contains all contacts, e-mail, mailbox, and .vcf vCard or VCF calendar is a file that acts as an electronic business card. When you receive an e-mail, you can open them and have the contact details entered into the Mail Client application.

Executable extensions

Extension Description .app Application or APP is a Mac OS application. These applications are actually directories with the extension of .App. .bat The batch file is a text file containing a series of commands. When starting the batch file these commands will be executed. .cgi Common Gateway Interface or CGI is executable file that is allowed to run on web server. .com This is an executable file for Dos & Windows operating systems. .exe This is an executable file for Dos & Windows operating systems. .pif Program Information File or PIF file is used to launch DOS program in Windows multi-tasking environment using certain settings. The .vbs file containing visual basic script can be done by double clicking on the file.

Windows extension

Extension Description .cpl Windows Control Panel File: Double clicking on this file will launch the linked control panel. Dynamic Link Library .dll or DLL is a shared library in Windows. Executable files will use these DLLs to run properly. .dmp File memory dump is the file created by Windows when the program fails. These memory dump files can be used to determine why a particular program failed. .lnk These file types are links or shortcuts to executable files that are located elsewhere on the Windows operating system. These .lnk files are just a pointer to the executable file and can be deleted without affecting the executable file itself. .msi File Windows Installer can be used to install applications on your computer. .reg File The Windows Registry is a file that can be used to make modifications to the Windows Registry. You should never double-click these files unless you are sure what you are doing. .sys File Windows driver is a file that allows Windows to communicate with the hardware installed on the computer .tmp A temporary file created by the program. These temporary files will be deleted automatically when the program is closed. They are safe to remove.

Installation extension

Extensions Description .cfg The configuration file contains configuration information about how a software will work. .conf Similar to .cfg .ini The initialization file contains the settings that the program will configure itself at the start.

Font extension

Extension Description .fnt file Windows font file: If you double-click this file type, you will be able to see specific fonts in many sizes. .fon Similar to .fnt .ttf File TrueType font: If you double-click this file type, you will be able to see specific fonts in many sizes.

Extensions of source programs and files

Extensions .asp Active Server Pages or ASP description is the file that contains the source code for Microsoft ASP server-side scripting language. .c File C contains the source code for the C .cpp programming language The CPP file contains the source for the C ++ programming language. .h Title file for C / C ++ programming language. .java Java file contains source file for JAVA programming language. .php The PHP file contains the source file for the PHP programming language. .pl The PL file contains the source file for the PERL programming language. .py The PY file contains the source file for the Python programming language. .xml Extensible Markup Language File: These file types show how text data is used by any program that supports XML language.

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